Reconstructive dentistry involves the checking of the occlusion of maxilla and mandible of the patient as well as the making of prostheses such as crowns, bridges and partial or full dentures. In this field of dentistry, measurements of the mandibular movements constitute an important stage of diagnosis and the proper adjustment of an articulator for each patient. However, in the absence of a simple method and apparatus for the accurate measurements of the mandibular movements, the dentist has to resort to a trial-and-error approach either by taking interocclusal record or tracing the three-dimensional locus of various points on the mandible with the aid of a pantograph. In the former method, the record is placed on a semi-adjustable articulator which is manipulated to obtain optimum fitting to the record. In the latter method, the trace is transferred to a fully adjustable articulator which is manipulated to obtain a faithful reproduction of the trace. These methods are lengthy and involve the dentist's experience and skill to avoid erroneous measurements. Therefor, they are not best suited to clinical purposes and are often omitted from the practice of reconstructive dentistry. However, the fact remains that dental practice must be based on the accurate measurements of the mandibular movements. Prostheses made without meeting this requirement fail to achieve the satisfactory mastication. Furthermore, defective prostheses may induce arthritis of the temporomandibular joint which is sometimes complicated with neurosis. The need for an early solution to these problems is increased as the preference of people for foods is diversified and their mean life is extended.
The inventors previously proposed a method and apparatus that provided the simple and accurate measurement of the mandibular movements by simply detecting the three-dimensional displacement of a certain point fixed to the front side of the anterior teeth in the mandible. The proposed apparatus includes a device which, while the mandible is moved under limited conditions, detects the three-dimensional displacement of specific point on the front side of the mandible and outputs the detected displacement information, and a memory that stores this displacement information and the data of the measurements of the size of the face including the mandible. The necessary data of the mandibular movement is obtained by performing operations on the three-dimensional displacement information for the specific point and the measured data of the facial size. Alternatively, the specific type of the mandibular movements is determined by making comparison with known data for the mandibular movements. Details of this technique are given in Japanese Patent Application (OPI) No. 163043/80 (the symbol OPI as used herein means an unexamined Japanese patent application) filed by the present inventors under the title "Apparatus for electronic measurements of the mandibular movements" and in Japanese Patent Application No. 80316/81 also filed by the same inventors under the title "Method and apparatus for determining the type of mandibular movements". An example of the "device which detects the three-dimensional displacement of a specific point on the front size of the mandible and outputs the detected displacement information" is the following: a point light source is mounted on the front end of the mandible of the patient; three units of one-dimensional light image detector are arranged in orthogonal directions in a fixed manner with respect to the maxilla and in proximity around said point light source; the position of said point light source is read by said three detectors in terms of one-dimensional light image signals in orthogonal directions and these signals are subsequently converted to three-dimensional displacement signals for the specific point at the front end of the mandible. A specific example of this appearance is shown in Japanese Patent Application (OPI) No. 116258/79 also filed by the present inventors.